8.5 Rule 5: Single source placement closer to an enclosure wall reduces EMI

Placement of a source closer to a metallic wall reduces the radiated emission from that source. This design guideline can be generalized to arbitrary metallic enclosures with apertures, even when the enclosure is large compared to the wavelength in each dimension. The electric field vanishes tangential to the wall and thus it decreases approaching the wall. Therefore, the coupling of a source, which is parallel to the wall must be reduced, when the source is placed closer to that wall.

\includegraphics[height=6.5 cm,viewport=180 285 415
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(a) Source variation in x-direction (ys=50mm). (b) Source variation in y-direction (xs=80mm).
Figure 8.8: Excitation of the enclosure with a single current of 10$ \mu $A supplied directly to the planes at the position ($ x_s$,$ y_s$).

C. Poschalko: The Simulation of Emission from Printed Circuit Boards under a Metallic Cover